Numerous processes are within the purview of those skilled in the art for the preparation of toners. Emulsion aggregation (EA) is one such method. These toners may be formed by aggregating a colorant with a latex polymer formed by emulsion polymerization. For example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety, is directed to a semi-continuous emulsion polymerization process for preparing a latex by first forming a seed polymer. Other examples of emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in U.S. Pat. Nos. 5,403,693, 5,418,108, 5,364,729, and 5,346,797, the disclosures of each of which are hereby incorporated by reference in their entirety. Other processes are disclosed in U.S. Pat. Nos. 5,527,658, 5,585,215, 5,650,255, 5,650,256 and 5,501,935, the disclosures of each of which are hereby incorporated by reference in their entirety.
Polyester EA toners have also been prepared utilizing emulsions prepared by solvent containing processes, for example, solvent flash emulsification and solvent-based phase inversion emulsification. In both cases, large amounts of organic solvents such as ketones or alcohols have been used to dissolve the resins. The solvents need to be evaporated at the end of the emulsification, which usually takes a long time to complete. Other drawbacks with these processes include: 1) the solvent containing process is not environmentally friendly; 2) waste treatment and solvent recovery adds extra cost to the EA toner process; and 3) the residual amount of solvent may vary, which will affect both the toner process and the toner produced by the process.
Accordingly, solvent-free emulsion processes have been developed such as solvent-free extrusion emulsification (SFEE) and solvent-free phase inversion emulsification (SFPIE). However, in such processes, crystalline polyester resin (CPE)—the key component in ultra low melt (ULM) emulsion/aggregation toner—can only be successfully emulsified using a high surfactant concentration which leads to significant difficulties with toner washing and higher triboelectric charge in the final toner. While not limited to any particular theory, it is believed that with high surfactant concentration, excess surfactant is trapped in the toner particle made with the solvent-free latex.
Additionally, rotor-stator type homogenizers have been widely used to prepare emulsions and dispersions. However, the particle size achievable with traditional rotor-stator homogenizers may not be as small as those with media mills or high-pressure homogenizers equipped with homogenizing valves or liquid jet interaction chambers.
Improved methods for producing toners, which reduce the number of stages and materials, remain desirable. Such processes may reduce production costs for such toners and may be environmentally friendly.